A metal material in which Young's modulus is lowered can obtain large elastic deformation with respect to load stress. Due to its flexible property, it is used for various purposes. For instance, when a metal material in which Young's modulus is lowered is used as a spring material, it is possible to downsize a spring since a winding number of the spring can be decreased. In addition, a metal material in which Young's modulus is lowered can improve usability when applying to glasses due to its flexible property. Moreover, a metal material in which Young's modulus is lowered can improve a flying distance when applying to golf clubs. Furthermore, such a metal material can be appropriately used for products such as robots and auxiliary materials for artificial bones.
For instance, metals such as iron and steel are used for hands and fingers of robots. However, when a robot is holding an object with its stainless-steel hand, there is a problem with the hand that tends to break the object since it is difficult to control a power to hold. Therefore, it is required that hands and fingers of robots are manufactured by use of materials capable of lowering stress effectively with low Young's modulus (stress-buffering materials). Also, when a metal with low Young's modulus can also lower a coefficient of linear expansion simultaneously, and, for instance, when the metal is used as components such as wiring members of a semiconductor module and various metal seals, the metal can be used as a stress-buffering material effectively absorbing thermal strain (thermal stress) caused by a difference of the coefficient of linear expansion from chips.
As described above, such a metal with low Young's modulus can be used for various purposes as a stress-buffering material. As a metal material with low Young's modulus, a titanium alloy and Ni—Ti shape memory alloy can be included, for instance. These are the metals based on titanium, and thus expensive. In addition, although Mg is a pure metal in which static Young's modulus is as low as 40 s GPa, a usage was limited due to low intensity, heat resistance, corrosion resistance, durability, and the like depending on purposes. Thus, it is required that a low elastic alloy based on aluminum that is relatively low-cost among metals is improved so as to be a material possible to be used as a stress-buffering material. As a low elastic material based on aluminum, an amorphous carbon fiber-reinforced aluminum composite material having a low elastic modulus is disclosed in Patent Citation 1, for instance.
However, the invention described in the above-mentioned Patent Citation 1 was unfavorable for mass production because of high production costs due to a composite material. Moreover, the invention described in Patent Citation 1 could not be used as a stress-buffering material for components of a semiconductor module (e.g. wiring members) and various metal seals, and the like.
The present invention has been made focusing on the above-mentioned problems. An object of the present invention is to provide a stress-buffering material composed of an aluminum alloy that is low-cost, can further expand its use in various fields, and has low Young's modulus in excess of a conventional level.    Patent Citation 1: Japanese Patent Unexamined Publication No. 2005-272945